Build and rebuild problem

I have 2 projects with Qt-creator C++. Let's call it project A and project B. Project A works fine. But project B is strange. Last week when I tried to debug it, it stuck. I re-saved the .pro file (not changing anything) and it works. But now every time I build and debug (which is build and run), qt does rebuild it all. It creates moc_blabla.o again every time I build it. So when I debug project B, qt rebuild it and run, not build and run. But in project A everything works fine. Project A.pro and project B.pro have the same architecture, no special configuration, all is default. Is there something wrong I did in project B? Is there a way I can do a normal build in project B again? PS: I didn't change anything in project setting.

clean all, run qmake, then build again and see if that resolves your problem.

Sometimes when I have odd problems like that with a project I've found deleting the .pro.user files and re-configuring the project seems to clear it up.